1. Field of the Invention
The present invention relates to a heat supply and electric power-generating fuel cell in which a body of a fuel cell incorporated into a fuel cell power generator is heated with hot water during starting to preheat the cell body and cooled by cooling water during power-generation to remove a part of the heat of reaction, whereby the temperature of the cell body is maintained at a constant level while supplying heat to users.
2. Description of the Prior Art
There has been known a fuel cell to be incorporated into a fuel cell power generator whose fuel cell body is cooled with cooling water to remove a part of the heat generated during the power-generation and to thus maintain the fuel cell body at a predetermined operating temperature and which can thus supply heat to users through the heat exchange between the cooling water thus heated and a proper heat transfer medium. The fuel cell is further equipped with a means for heating, with hot water, the fuel cell body up to a temperature suitable for the cell reaction during starting of the fuel cell. FIG. 1 is a system diagram showing a fuel cell power generator provided with such a conventional fuel cell.
In FIG. 1, a fuel cell body 1 is schematically depicted and has a plurality of units cells, which are put on top of each other and each comprises a fuel electrode 2, an oxide electrode 3 and a phosphoric acid electrolyte layer (not shown) sandwiched between these electrodes, and a cooling plate 5 having with cooling pipes 4 which are provided for every unit cells and serve as water flow paths.
In a fuel-reforming apparatus 7, a starting gas such as a natural gas supplied thereto through a fuel supply system 8 is heated by water vapor supplied from a water vapor separator 21, as will be detailed below, through a water vapor supply system 10 as well as the heat generated during combustion of an off-gas in a burner (not shown) in the presence of a reforming catalyst, as will be detailed below, to give a reformed gas rich in hydrogen.
The fuel cell body 1 and the fuel reforming apparatus 7 are communicated to one another through a reformed gas supply system 11 and an off-gas supply system 12 to form a circulation system for the reformed gas, the reformed gas supply system serving as a means for supplying the reformed gas generated in the fuel-reforming apparatus 7 to the fuel electrode 2 of the fuel cell body 1 and the off-gas supply system serving as a means for supplying an off-gas including hydrogen gas, which is discharged from the fuel electrode 2 and does not take part in the cell reaction, to the burner of fuel-reforming apparatus as a fuel.
Moreover, the fuel cell body I is connected to an air supply system 14 having a blower 13 for supplying air to the oxide electrode 3 and an air exhaust system 15 for evacuating the air used in the cell reaction. Reference numeral 16 represents a thermometer for detecting the temperature of the fuel cell body 1.
To circulate cooling water through the fuel cell body 1 during power-generation, the cooling pipes 4 fitted to the cooling plate 5 of the fuel cell body 1 are connected to a water-circulation system 20 which has water vapor separator 21, a pump 22 for circulating the cooling water and a heat exchanger 23 for recovering heat.
The water vapor separator 21 serves to separate water vapor from the water discharged from the cooling pipes 4 of the fuel cell body 1. The water vapor separated is transferred to the fuel-reforming apparatus 7 through the water vapor supply system 10 in which it is admixed with a starting fuel. Reference numeral 24 represents a thermometer for detecting the temperature of the water in the water vapor separator 21.
The heat exchanger 23 for recovering heat serves to recover the heat of the water having an elevated temperature. In the heat exchanger 23, the temperature of a heat transfer medium to be supplied to users is raised through the heat-exchange with the heated cooling water and the heat transfer medium is supplied to the users through a heat transfer medium supply system 25.
In addition to the water-circulation system 20, the water vapor separator 21 further has a water-circulation system 31 for starting the fuel cell body, which serves to supply the water separated in the water vapor separator 21 to a circulating pump 27 for starting through a heat exchanger 30 for heating which comprises a heat exchange part 29 having a heating burner 28 and to then return the water to the water vapor separator 21.
In the heat exchanger 30 for heating, the fuel fed thereto through a fuel supply system 32 is combusted by the heating burner 28 while supplying a combustion air fed thereto through a combustion air supply system 33 and the temperature of the water fed to the heat exchanger is raised through the heat exchange between the heat transfer medium generated during the combustion and the water.
Upon starting a fuel cell having such a structure, the circulating pump 27 for starting the cell of the system 31 for circulating the starting water is started and simultaneously the combustion of the fuel is started by igniting the heating burner 28, whereby the water in the water vapor separator 21 is circulated along the system 31 for circulating the starting water and simultaneously heated to 170.degree. C. by the action of the heat generated during combustion of the fuel in the heating burner 28 to give water vapor.
The pump 22 for circulating cooling water during operation of the system 20 is operated to circulate the heated water in the water vapor separator 21 through the system 20 for circulating water for operation and the cooling pipes 4 within the cooling plate 5 of the fuel cell body 1 to thus heat fuel cell body 1 and raise the temperature of the cell body up to a level suitable for progressing the cell reaction. After completion of the desired temperature rise, the circulating pump 27 for starting the cell and the heating burner 28 are stopped.
At the time when the temperature of fuel cell body 1 reaches a desired level, the reformed gas generated in the fuel-reforming apparatus 7 is fed to the fuel electrode 2 through reformed gas supply system 11, while air is supplied to the oxide electrode 3 by the blower 13 through the air supply system 14 and thus the fuel cell body 1 causes the cell reaction to produce electric power. The heat generated during the cell reaction is removed by the water circulating through the water-circulation system 20 for operation and correspondingly the temperature of the fuel cell is maintained at a predetermined level.
The off-gas generated during the cell reaction is fed to the burner of the fuel-reforming apparatus 7 through the off-gas supply system 12 while exhaust air used in the cell reaction is released in the air through the air exhaust system 15.
Incidentally, the water whose temperature is raised through the cooling of fuel cell body 1 transfers heat to a heat transfer medium such as water through heat-exchange within the heat exchanger 23 for recovering heat and the heat transfer medium thus heated to an elevated temperature is supplied to users in the form of steam.
When a fuel cell having the foregoing structure produces electric power and simultaneously provides heat by making use of the heat of reaction during the power-generation, a desired quantity of heat must always be supplied to the fuel cell to produce a predetermined quantity of electric energy. For this reason, for instance, the temperature and pressure of the steam as a heat transfer medium to be supplied to users are controlled to predetermined ranges respectively. In such a heat supply and powergenerating system, however, a demand for heat is not always proportional to that for generated energy. For instance, if the demand for heat is lower than that for electric power, users must deal with the excess or residual heat. On the other hand, even if the demand for heat is greater than that for the electric power, the temperature and pressure of the steam to be supplied to users are controlled to predetermined ranges for preventing any reduction in the operating temperature of the fuel cell. This leads to a limitation in the quantity of heat to be supplied.
If the temperature and pressure of the steam are not controlled to predetermined ranges and the operating temperature of the fuel cell is dropped because of an increase in heat used by users over the heat of reaction generated during the power-generation, the desired temperature of fuel cell body 1 may be maintained by heating the water in the water vapor separator 21 through the operation of the pump 27 for circulating the starting water and heating burner 28. In this case, however, this operation results in a delay of the response of the fuel cell for a time required for raising temperature to a desired level due to the high heat capacity of the water. More specifically, it takes a long time period from the detection of the temperature drop in the fuel cell till the operation temperature thereof reaches the predetermined level by operating the heating burner.
In general, the fuel cell power generator requires a large area for establishment per unit output as compared with other kinds of power generators. Accordingly, there has been a demand for making the generator more compact through elimination of unnecessary parts and/or integration of two or more of parts.